1. Field of the Invention
The present invention relates to an image forming apparatus with a detachable humidity detector unit which requires no adjustment after its installation in the apparatus.
2. Description of the Related Art
Conventionally, a humidity detector and a temperature detector are provided to detect the accurate relative humidity in the vicinity of a photosensitive drum in a color laser printer. A temperature-oriented change in the detection output of the humidity detector is compensated for with the temperature detected by the temperature detector. The humidity and temperature detectors are constituted integrally and are coupled to a temperature compensator.
The humidity detector will deteriorate even when not supplied with electricity. Its service life is about 10,000 hours (1 to 1.5 years). This service life is shorter than that of the image forming apparatus, and the humidity detector often needs replacing. Since the temperature detector is a thermistor or the like, its service life is as long as that of the image forming apparatus. The humidity detector and temperature detector are integral. Thus when the life of the humidity detector expires and needs replacing, the temperature detector, which requires no replacing yet must also be replaced at the same time. This is very uneconomical.
The temperature detector and the humidity detector cannot meet the exact specifications, due to changes of the conditions, though slight, in which they have been made. Consequently, the temperature detector fails to output a voltage which accurately corresponds to the ambient temperature, and the humidity detector fails to output a voltage which accurately corresponds to the ambient humidity. Inevitably, it is necessary to adjust these detectors, so that they output voltages exactly corresponding to the temperature and humidity.